1. Field of the Invention
The present invention relates, in general, to a nozzle for injection molding machines used for injecting a molten plastic material into a cavity of molds during an injection molding process and, more particularly, to an injection nozzle having a guide slot at its top end portion and movably receiving a pin actuating bar, integrated with the valve pin of a valve system provided around the top end portion of the nozzle, in the guide slot, thus allowing a precise vertical movement of the valve pin in the nozzle and reducing the size of the nozzle, and almost completely preventing undesired malfunction or breakage of the valve pin.
2. Description of the Prior Art
As well known to those skilled in the art, in order to produce plastic products in large quantities using an injection molding machine, a molten plastic material is injected into a cavity of molds from an injection cylinder of the molding machine through both a manifold and a runner bush provided in a runner. After the plastic material, received in the cavity of the molds, is completely solidified into a plastic product, the molds are opened by a separate mold opening device, thus allowing the plastic product to be removed from the molds. The runner bush of a runner is typically and interiorly provided with a shut-up nozzle or an on/off nozzle for selectively closing the gate of the cavity, thus controlling an injection of molten plastic material into the cavity while selectively closing the gate of the cavity. However, when the gate of the cavity is closed by such a typical shut-up nozzle or a typical on/off nozzle, the molten plastic material, retained in a position around the gate, may fail to be completely solidified at a time a plastic product is removed from the molds. Such an incompletely solidified plastic material is thus taken out of the molds along with the plastic product when the product is removed from the molds. The incompletely solidified plastic material regrettably leaves a sprue or a slug on the plastic product and forces an additional process to be performed to remove such sprues from plastic products. This is inconvenient to users of injection molding machines and reduces the quality of injection molded plastic products.
In an effort to overcome the above problems, the inventor of this invention proposed valve systems for controlling the nozzles of injection molding machines in Korean U. M. Registration Nos. 96,556 and 116,226. The valve system, disclosed in the document of No. 96,556, is installed at a position above the manifold of a runner. The above valve system is designed to start to lower its valve pin so as to close the outlet end of an injection nozzle after a molten plastic material is completely injected into a cavity of molds. The valve system thus prevents a further injection of the molten plastic material from the injection nozzle into the cavity. In such a case, the lower end of the valve pin closes the outlet end of the injection nozzle, thus allowing the injection molded plastic products to be free from sprues. On the other hand, the valve system of No. 116,226 is designed to overcome problems experienced in the valve system of No. 96,556. In order to accomplish the above object, the valve system of No. 116,226 is installed at a side of the nozzle. The above valve system has a piston, while the injection nozzle has a valve pin with the valve pin being connected to the piston of the valve system using a linkage. When the piston of the valve system is moved in a vertical direction, the vertical moving action of the piston is transmitted to the valve pin through the linkage, thus allowing the valve pin to move in the same direction. The valve system of No. 96,556 is more preferably used with an injection molding machine capable of producing large-scaled plastic products or producing plastic products in large quantities. On the other hand, the valve system of No. 116,226 is more preferably used with a small-sized injection molding machine suitable for producing small-scaled plastic products.
However, the valve system of No. 96,556 is problematic in that a manifold has to extend between the valve system and the injection nozzle, thus inevitably having a long valve pin. Such a long valve pin enlarges the size of the manifold, thus requiring a large area for the manifold and finally enlarging the size of the molds. In addition, it is also necessary to always retain the molten phase of the plastic material in the manifold during an injection molding process. This forces a heater to be installed in the manifold so as to heat and melt the plastic material in the manifold. However, such a heater undesirably and thermally expands the manifold, thus undesirably changing the position of the manifold with both the valve system and the injection nozzle being retained at a fixed position. In such a case, the valve system cannot be operated, thus preventing an injection molding process from being continuously performed for a lengthy period of time. In addition, since the valve system and the injection nozzle are provided at both sides of the manifold, the plastic product removing direction from the molds is fixed to one direction. This forces a user of an injection molding machine to add another manifold when the user manufactures plastic products through a stack molding process wherein the plastic products have to be removed from the molds in opposite directions. Therefore, it is very difficult to use the above valve system in such a stack molding process. In addition, the valve system of No. 96,556 reduces productivity and work efficiency while producing plastic products through an injection molding process. On the other hand, the valve system of No. 116,226 is problematic in that it is installed at a side of the injection nozzle, thus being free from enlarging the size of the manifold different from the valve system of No. 96,556. However, this valve system is problematic in that it causes the size of the injection nozzle to be enlarged. In addition, since the valve pin is connected to the valve system through a linkage, it is somewhat difficult to stably and precisely move the valve pin in a vertical direction. Therefore, the valve pin may fail to precisely move in the vertical direction, thus reducing work efficiency during an injection molding process.
Since the valve system of No. 96,556 has a large size, thus being somewhat effectively used in producing a large-scaled plastic product which has to be molded using molds having a plurality of gates for the cavity. However, it is almost impossible to use the above valve system in producing small-scaled plastic materials. On the other hand, the valve system of No. 116,226 is somewhat preferably used in producing small-scaled plastic products or one plastic product. However, it is almost impossible to use this valve system in producing large-scaled plastic products or producing plastic materials in large quantities. Therefore, the two valve systems, disclosed in Korean U. M. Registration Nos. 96,556 and 116,226, force a user of an injection molding machine to have separate molding machines so as to manufacture plastic products regardless of sizes or quantities of resulting products. This is inconvenient to the users of the injection molding machines and reduces compatibility of the injection nozzles for the molding machines.